Printer Driver dead after restart

Our new Windows 7x64 printer driver roughly based on pjlmon from the Windows dev kit works once on install - receiving EnumPorts and then OpenPort after the install. But after a reboot (or net stop/start spooler) it receives only the initial EnumPorts with 0 buffer size, and nothing else. There is no debug available form Windows as to why it goes no further, and nothing crashes. The spooler is not locked, just not taking any further interest.

Has anyone seen anything like this? I suspect it is registry linked, but all looks ok. The printer status is on-line according toW Windows, and the port driver is essentially just writing to file, not to a physical device.